U.S. patent number 9,247,995 [Application Number 14/532,236] was granted by the patent office on 2016-02-02 for tattoo removal with two laser beams via multi-photon processes.
This patent grant is currently assigned to Trustees of Princeton University. The grantee listed for this patent is Szymon Suckewer. Invention is credited to Szymon Suckewer.
United States Patent |
9,247,995 |
Suckewer |
February 2, 2016 |
Tattoo removal with two laser beams via multi-photon processes
Abstract
A method for removing tattoos using two laser beams and a
multi-photon process is disclosed. A 0.1 to 100 nsec pulse
secondary laser beam focused to 10.sup.8 W/cm.sup.2 creates a
temporary channel from the skin surface to the tattoo pigment. A
100 fsec pulse main laser beam is then guided through the channel
to the pigment and focused to sufficient intensity, i.e., 10.sup.12
W/cm.sup.2 or more, to initiate a multi-photon process that breaks
up the pigment, disrupting its light reflecting properties. The
channel allows the main laser beam unobstructed passage to the
pigments, resulting in efficient use of the main laser. The pigment
fragments escape through the temporary channel or diffuse into the
blood stream. A suitably configured Ti/Sapphire laser beam is split
into two components, with an uncompressed component used as the
secondary laser beam, and a compressed component as the main laser
beam.
Inventors: |
Suckewer; Szymon (Princeton,
NJ) |
Applicant: |
Name |
City |
State |
Country |
Type |
Suckewer; Szymon |
Princeton |
NJ |
US |
|
|
Assignee: |
Trustees of Princeton
University (Princeton, NJ)
|
Family
ID: |
48695453 |
Appl.
No.: |
14/532,236 |
Filed: |
November 4, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150057645 A1 |
Feb 26, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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13781287 |
Feb 28, 2013 |
8915907 |
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13460442 |
Apr 30, 2012 |
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12136943 |
May 29, 2012 |
8187256 |
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60953826 |
Aug 3, 2007 |
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60944338 |
Jun 15, 2007 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61B
18/203 (20130101); A61B 18/20 (20130101); A61B
2017/00769 (20130101); A61B 2018/00452 (20130101); A61B
2018/00577 (20130101); A61B 2018/00458 (20130101); A61B
2018/207 (20130101); A61B 2018/2025 (20130101) |
Current International
Class: |
A61B
18/20 (20060101); A61B 17/00 (20060101); A61B
18/00 (20060101) |
Field of
Search: |
;606/9 ;607/88 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Thomson; William
Assistant Examiner: Lipitz; Jeffrey
Attorney, Agent or Firm: Rosser; Roy
Parent Case Text
CLAIM OF PRIORITY
This application is a continuation of U.S. patent application Ser.
No. 13/781,287 which in turn is a continuation in part of U.S.
patent application Ser. No. 13/460,442 filed on Apr. 30, 2012 by
Smits et al. entitled "Tattoo Removal and Other Dermatological
Treatments using Multi-photon Processing" is a continuation of U.S.
patent application Ser. No. 12/136,943 filed on Jun. 11, 2008 by
Smits et al. titled "Tattoo Removal and other Dermatological
Treatment using Multi-photon processing" that issued as U.S. Pat.
No. 8,187,256 on May 29, 2012, the contents of all of which are
hereby incorporated by reference.
This application is further related to, and claims priority from,
U.S. Provisional Patent application No. 60/944,388 filed on Jun.
15, 2007 by Smits et al entitled "Tattoo Removal and other
Dermatological Treatment using Multi-photon processing" and to U.S.
Provisional Patent application No. 60/953,826 filed on Aug. 15,
2007 by Smits et al entitled "Tattoo Removal and other
Dermatological Treatment using Multi-photon processing" the entire
contents of both of which are hereby incorporated by reference.
Claims
What is claimed:
1. A method of removing pigment from beneath the surface of the
skin, comprising: creating a temporary channel from said surface of
the skin to a vicinity of said pigment by ablating material using a
first laser beam emanating from a laser, said first laser beam
having a pulse length in a range from 0.1 nsec to 100 nsec and,
being focused to have an intensity in a range of 10.sup.7 to
10.sup.10 W/cm.sup.2 within a focal regions; directing through said
temporary channel to said vicinity of said pigment, a second laser
beam emanating from said laser or from a second laser, said second
laser beam having a pulse length of 400 fsec or less and being
focused to have an intensity of at least 10.sup.12 W/cm.sup.2 in a
focal region, thereby initiating a multi-photon ablation process in
said vicinity of said pigment, and breaking said pigment into two
or more constituent parts.
2. The method of claim 1 wherein an optical system is used to align
said focal region of said first laser beam, when focused to have an
intensity in a range of 10.sup.7 to 10.sup.10 W/cm.sup.2, and said
focal region of said second laser beam emanating from said laser or
said second laser when focused to have an intensity of at least
10.sup.12 W/cm.sup.2, to substantially coincide.
3. The method of claim 1 wherein said pigment comprises tattoo
ink.
4. The method of claim 1 wherein when focused to have an intensity
of at least 10.sup.12 W/cm.sup.2, said beam emanating from said
lasers have a pulse energy equal to or smaller than 10 mJ.
5. The method of claim 1 wherein said pigment is a granule of
pigment of a tattoo; and further comprising repeating breaking said
granules of pigment of said tattoo until said tattoo is
substantially invisible.
6. The method of claim 1 further comprising a covering a patient's
skin surface in a vicinity of said temporary channel with a layer
of water-impermeable material that is substantially transparent to
said first and second laser beams emanating from said one or two
lasers.
7. The method of claim 6 wherein said water-impermeable material is
a sheet of mica having a thickness of 300 .mu.m or less.
Description
FIELD OF THE INVENTION
The present invention relates to procedures and devices for
dermatological treatment using multi-photon processing, and more
particularly to methods and apparatus for tattoo, pigment, and
blemish removal. The invention preferably includes uses 2 laser
beams, one of ultra-short pulse durations, typically 50 to 100
femtoseconds (1 femtosecond=1 fsec=1.times.10.sup.-15 sec) and of
very high intensity, 1012 W/cm.sup.2 or greater, with a preferable
intensity in the range of 10.sup.13-10.sup.15 W/cm.sup.2, for
removal of pigments by multi-photon processing (the "Main Laser"),
and a second laser beam (the "Secondary Laser"), of much longer
pulse duration, about thousands to hundreds of thousands longer
pulses, and hence with a much lower intensity, which sufficiently
creates a channel in the skin for the Main Laser beam to propagate
toward the pigment with minimum loss of intensity during
propagation in said channel.
Although intensities of the Main Laser pulses are very high, the
energy of each pulse may be low due to the short pulse duration, in
the range of about 0.5 mJ to 20 mJ per pulse, although at a lower
repetition rate of about 10 Hz a higher range of energy per pulse
could be used, and at a higher repetition rate of 1 kHz, lower
range of energy per pulse could be used.
BACKGROUND OF THE INVENTION
Tattooing is accomplished by injecting colored pigment into small
holes made in the skin at various depths. The most common are
"professional tattoos" with depth of holes approximately 2 to 2.5
mm and "amateur tattoos" with depth of holes approximately 1.5 mm.
Tattoos may have a wide range of colors and are relatively
permanent.
With the rapidly growing number of people who are acquiring
tattoos, many may want to later have them removed. There is,
therefore, a significant demand for the removal of tattoos. Tattoo
removal, however, is not easily accomplished. In tattooing,
pigments are injected into the dermis, the layer of skin that lies
immediately beneath the approximately one millimeter thick
epidermis, which is the dead, external surface layer of the skin.
The injected pigments initially tend to aggregate in the upper
dermis, close to the epidermis. One method of physically removing
tattoos, therefore, requires abrading away the entire epidermis
immediately above the tattoo pigment. This is a painful process,
which usually leave the subject with significant scarring. Over
time, the tattoo pigments may become encapsulated in fibroblasts
and migrate deeper into the dermis so that older tattoos, while a
little duller, are even more difficult to remove by abrasion.
With the advent of high power lasers, an alternative, non-abrading
method of removing tattoos, which relies on thermal photoablation,
became possible. In this method, the laser wavelength is chosen so
that the tattoo pigment absorbs the laser light more readily than
the surrounding skin. The laser pulses are then made powerful
enough so that the pigment heats up sufficiently to thermally
photoablate, i.e., dissociate, into small fragments. These
fragments are typically transported out of the dermis by
macrophages or diffusion into streams of blood and are distributed
in the patient's body.
Tattoo pigments, however, cover a range of colors, including black,
white, blue, red, green, and others. Dark blue-black amateur and
professional tattoos usually contain amorphous carbon, graphite,
India ink, and organo-metallic dyes. There has been, therefore, no
single laser most suitable for tattoo removal by thermal
photoablation.
Laser-based tattoo removal, therefore, has been accomplished using
a variety of lasers to induce thermal photo-ablation, including,
but not limited to: Q-switched Nd:Yag lasers typically operating at
1064 nanometer (1 nanometer=1 nm=1.times.10.sup.-9 m) or 532 nm,
with 5-20 nanoseconds (1 nanosecond=1 nsec=1.times.10.sup.-9 sec)
pulse duration; Q-switched Alexandrite lasers typically operating
at 755 nm, with 100 nsec pulse duration; and Q-switched Ruby lasers
typically operating at 694 nm, with 20-40 nsec pulse duration.
These lasers are collectively known as nsec-type lasers. Typically,
a cream to numb the skin is applied to the patient prior to the
treatment to reduce the level of pain felt during the treatment.
Pulses of the laser light, typically of the order of 5 to 100 nsec,
are then directed through the surface of the subject's skin and are
absorbed by the tattoo pigment. The light breaks the pigment into
particles by thermal photoablation. The particles are small enough
to be absorbed by the body.
The principal sources of trauma in the nsec laser removal of
tattoos are the heating of the skin, which causes damage similar to
a second-degree burn, and the formation of highly localized shock
waves in the dermis that cause undesirable tissue damage. Even with
the use of numbing agents, the patient normally experiences pain
during the treatments. After each treatment, the body's scavenger
cells remove the particles of pigment from the treated pigmented
areas. The skin and tissue damage then heals over the next several
weeks, although healing time varies depending upon the size and
depth of the tattoo, the procedure used and the patient's healing
process. More than a dozen treatments, which can span over 1 year
or more, may be necessary to complete the process. Some scarring or
color variations are likely to remain.
These current laser procedures for tattoo removal are painful,
expensive, rarely 100% effective, may leave permanent scarring, and
typically require multiple treatments spread over a long period of
time.
Because of the problems related to the prior art, improvements in
tattoo and pigment removal systems and methods are needed that more
completely remove tattoos, pigments, and blemishes, do not leave
permanent scarring, do not cause burning, reduce or eliminate pain,
and may be accomplished with fewer treatments spanning a shorter
total time period.
SUMMARY OF THE INVENTION
Briefly described, the present invention provides methods and
apparatus for tattoo, pigment, and blemish removal, and other
dermatological treatments, preferably via multi-photon processing.
The current invention preferably utilizes two laser beams, one to
create a channel beginning at the top layer of the skin and ending
in the vicinity of the pigment targeted for removal (the "Secondary
Laser"), and another laser beam that passes through said channel
and ablates said pigments (the "Main Laser"). These two beams can
be directed to the patient's skin at approximately the same time,
or where one is in advance of the other, depending on factors that
include skin type, skin conditions, and pigment types.
The channel created by the Secondary Laser acts as a waveguide for
the Main Laser toward the pigments, thus minimizing Main Laser
pulse energy loss and allowing for a lower Main Laser entrance
intensity. The channel also allows for ablated pigments and
material to escape from the skin.
It is an object of the invention to provide improved techniques of
removing tattoos, pigments, and blemishes from skin where burning
of the skin, scarring of the skin, and pain are minimized through
the use of a laser multi-photon processing.
It is another object of the invention to provide improved
techniques of removing tattoos, pigments, and blemishes from skin
where removal can be accomplished in fewer treatments over a
shorter period of time than prior methods.
It is another object of the invention to provide improved
techniques of removing tattoos, pigments, and blemishes from skin
where the channel created by the Secondary Laser allows for the use
of a lower intensity Main Laser.
It is another object of the invention to provide improved
techniques of removing tattoos, pigments, and blemishes from skin
where the ablated matter may escape from the skin via the channel
that the Secondary Laser created.
It is another object of the invention to provide improved
techniques of removing tattoos or pigments from skin where a laser
of a single wavelength can remove said tattoos or pigments
regardless of color.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a schematic overview of a system and method of
removing a tattoo using a two laser protocol of the present
invention.
FIG. 2 shows a schematic view of a laser pulse.
FIG. 3 shows a schematic view of an optical system of a preferred
embodiment of the present invention.
FIG. 4 shows a schematic view of an optical system of a further
preferred embodiment of the present invention.
FIG. 5 shows a schematic view of an optical system of yet another
preferred embodiment of the present invention.
FIG. 6 shows a close up schematic cross-sectional view of two laser
tattoo removal in accordance with the present invention.
FIG. 7 shows a close up schematic cross-sectional view of two laser
tattoo removal in accordance with a further embodiment of the
present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention relates to methods and apparatus for
dermatological treatment that use multi-photon processing events as
well as channel creation to reach material to be treated or
removed. In particular, the present invention is directed to
tattoo, pigment, and blemish removal using two lasers, a Secondary
Laser, which creates a channel within the skin, and a Main Laser,
which passes through said channel and removes pigments or material
using multi photon ablation. These two beams may be directed to the
patient's skin coaxially at approximately the same time, or where
one is in advance of the other, depending on factors that include
skin type, skin conditions, and pigment types.
The Secondary Laser
A purpose of the Secondary Laser is to create a channel that may
begin at the outermost layer of skin and terminate in the area of
the skin where material, such as tattoo ink or pigmented skin, is
targeted for ablation. This Secondary Laser has a preferred pulse
duration of 1 to 20 nsecs, although a range of 0.1 to 100 nsec may
be used, and its pulse duration may be 1,000 to 100,000 longer than
that of the Main Laser, and hence at a much lower power. While the
preferred focal spot diameter for the Secondary Laser may be from
50 to 250 micrometers, its focal spot diameter must be large enough
to create a channel so that the Main Laser may pass through the
channel, preferably 2 to 3 times larger than the diameter of the
Main Laser's focal spot. The preferred intensity of the Secondary
Laser is in the range of 10.sup.8 to 10.sup.9 W/cm.sup.2, although
a range of 10.sup.7 to 10.sup.10 W/cm.sup.2 may be used but may
produce less optimal results. A laser beam with a 1064 nm
wavelength may be used, although other wavelengths may also be
used. Repetition rates of 5 to 100 Hz are preferred, although
repetition rates up to a range of 1 kHz may be used but may have
less optimal results. By way of example, an Nd/YAG laser system may
play the role of the Secondary Laser.
The channel that the Secondary Laser creates may provide a
waveguide for the Main Laser to reach the targeted material,
whereby energy losses of the Main Laser's pulses are reduced and
may be minimized. Thus, a lower energy Main Laser may be used in
contrast to when no channel is created. Additionally, ablated
material, such as ablated ink pigments, may escape the body via the
channel.
The Main Laser
The Main Laser beam may enter the channel created by the Secondary
Laser, reach the material to be ablated, and ablate the material.
Preferably, the Main Laser will be a femtosecond laser with: a
relatively low energy, for example in the range of 2 to 5 mJ/pulse;
a pulse duration in the range of 50 to 100 fsec, although a range
of 10 to 500 fsec is possible; a focal spot diameter in the range
of 30 to 80 micrometers, although the diameter could be smaller or
greater depending on the focal spot diameter of the Secondary
Laser; and a preferred intensity in the range of 10.sup.13 to
10.sup.15 W/cm.sup.2, although a range of 10.sup.12 to 10.sup.16
W/cm.sup.2 may be used. The Main Laser beam's wavelength is
preferably 800 nm, although it may have a different wavelength.
Repetition rates of 5 to 100 Hz may be used, although repetition
rates up to 1 kHz may also be used. By way of example a Ti/Sapphire
laser system may play the role of the Main Laser.
In a preferred embodiment, the Main Laser's ultrashort and
ultraintensive beam may initiate multi-photon processes, also
called here multi-photon ablation, that may break down the targeted
material, such as pigment inks, and associated molecular bonding
without providing significant heat or local skin burning. Broken
down pigments and molecules may escape from the skin through the
channel and/or by moving down to the flow of blood. Multiple
treatments of the targeted treatment areas may therefore be
completed in significantly shorter intervals compared to thermal
laser-based tattoo removal treatments where burns caused by the
laser treatment must be given time to heal between treatments.
In contrast to a thermal ablation process, which is typically
generated by relatively low intensity but relatively high energy
laser pulses that may initiate a single-type photon absorption
process, multi-photon processing or ablation, utilizes a very
high-intensity laser pulse, i.e., many photons in a small volume at
the same time, where the density of photons is so great that during
an absorption event many photons are absorbed simultaneously, which
means that these many photons are absorbed by a particle, such as a
molecule, atom, or ion, in a time period that is shorter than the
relaxation time of the given particle.
Multi-photon processing also differs from thermal photoablation in
that the low amount of energy per pulse involved in multi-photon
processing allows the ablation to be very localized, very fast and
result in no or negligible thermal heating or shocking of any
surrounding material. For instance, by focusing a 2 mJ pulse of
laser light that has a temporal pulse length in the range from 100
to 300 femtoseconds in duration--although the pulse duration could
be shorter, for example 10 fsec, or longer, for example 500
fsec--to a small enough focal spot so the intensity is equal to or
greater than 10.sup.12 Watts/cm.sup.2, a multi-photon processing
event may be initiated. This may result the pigment materials being
broken into very small particles and in the dissociation of
molecules. Such pulses may be obtained from, for instance, a
suitably configured Titanium doped Sapphire (Ti:Sapphire) solid
state laser.
The number of photons absorbed simultaneously by the particles in
multi-photon ablation may be in the range of 5 to 10 photons per
particle on the low end, and 100 photons or more per particle on
the high end. The density of photons in a pulse is so high that the
number of photons absorbed simultaneously is very large; hence
multi-photon ablation may occur even where the energy of the pulse
is low, in the range of 2 to 5 mJ or less. This amount of energy is
sufficiently low that little or no damaging thermal heating of the
surrounding tissue occurs as the energy diffuses. This is in marked
contrast to thermal ablation with low-intensity pulsed lasers where
only a single photon is absorbed in any given absorption event, and
the pulse energy necessary for photoablation is so high that
damaging heating of the surrounding tissue occurs as the heat
diffuses.
"Few photon processes", for example, processes that involve not
more than 2 to 3 photons in a single absorption event, also tend to
result in thermal ablation, even though few-photon processes are
sometimes inaccurately labeled "multi-photon processes" in some
literature.
For a multi-photon process to be useful for treating skin
discolorations and tattoos, the intensities of the laser pulses
have to be very high. One way to simultaneously achieve both the
high intensity and low energy is by using ultra-short laser pulses.
In laser physics, ultra-short pulses are typically defined to be
pulses up to 10 psec in duration, but preferably 50 to 100 fsec or
even shorter. Moreover, the multi-photon ablation process is
practically independent of the pigment color as the process does
not depend on differential absorption by the pigment. Using
multi-photon processing to remove pigment from the skin does not,
therefore, require using different laser wavelengths for different
pigments. This is in sharp contrast to thermal photo-ablation
processes where the wavelength has to be chosen carefully to
maximize the interaction with the specific pigment, or pigments,
used in the tattoo, while allowing for sufficient dermal
penetration to reach the pigment and at the same time avoiding
absorption in the natural skin pigment, the melanin.
In the present invention, the channel in the skin, created by the
low intensity Secondary Laser beam and that leads towards the
pigment, or tattoo ink, may allow the very high intensity Main
Laser to be rapidly delivered to the pigment.
When the two laser wavelengths used in the present invention are in
the infra-red, they can penetrate deep into the dermis. The
necessary high intensities on the target material may therefore be
accomplished by using, for instance, a short focal length lens to
focus the laser beams directly on the pigment, while the Secondary
Laser low intensity laser beam may be focused with a longer focal
length to create an elongated channel in the skin directly to the
location of the pigments. By adjusting the Main Laser beam
intensity by altering the focal spot on the pigments, the intensity
within the focal volume can exceed the threshold intensity
necessary to initiate multi-photon processing.
Preferred embodiments of the invention will now be described in
detail by reference to the accompanying drawings in which, as far
as possible, like elements are designated by like words and
numbers.
Although every reasonable attempt is made in the accompanying
drawings to represent the various elements of the embodiments in
relative scale, it is not always possible to do so with the
limitations of two-dimensional paper. Accordingly, in order to
properly represent the relationships of various features among each
other in the depicted embodiments and to properly demonstrate the
invention in a reasonably simplified fashion, it is necessary at
times to deviate from absolute scale in the attached drawings.
However, one of ordinary skill in the art would fully appreciate
and acknowledge any such scale deviations as not limiting the
enablement of the disclosed embodiments.
There are at least two preferred embodiments of the invention. One
embodiment provides an optical device for the Main Laser beams and
Secondary Laser beams with the same wavelength, for example,
Ti/Sapphire laser with wavelength of 800 nm (1 nm=10.sup.-9 m),
which compressed (fsec) and uncompressed (sub-nsec) beams have the
same wavelength of 800 nm. In such a configuration, both beams are
directed to an optical system, their expenders and two spherical
lenses. One lens, the role of which may be to focus nsec- or
sub-nsec-type pulses of the Secondary Laser beam, may have a hole
in its center. The hole may be sufficient in diameter to allow the
Main Laser Beam to propagate through the lens's hole without
obstruction and to be focused at the same skin spot where the
Secondary Laser beam is focused. In some cases, when it is
necessary to create a longer channel in the skin toward a pigment,
for instance where a "professional" tattoo must be reached, then
the spherical lens with hole may be replaced by a conical lens (so
called "axicon") which also have a hole in its center to allow
propagation of the Main Laser beam pulses to occur without
obstruction.
The second embodiment provides an optical device where the Main
Laser beams and the Secondary Laser beams are of two different
wavelengths. The preferable optical device may consists of two
spherical lenses without holes, one said lens for focusing the
Secondary Laser beam and the second lens for focusing the Main
Laser beam. The Secondary Laser beam may be well reflected by
interferometric mirror, whereas the Main Laser beam, with a
significantly different wavelength, may pass through the mirror
with only minimal absorption of its energy. As in the first
embodiment, the lens for focusing the Secondary Laser beam pulse
may be replaced by an axicon in order to create a longer channel in
the skin toward a pigment of the tattoo.
By using a relatively high-repetition rate femtosecond laser, and
repeating the localized, multi-photon process event initialization
along the location of the pigment, that may, for instance, be a
tattoo, the entire tattoo may be removed with little or no damage
to the surrounding tissue. This process may be accomplished
manually, or under the guidance of a computer, or through a
combination thereof.
These and other features of the invention will be more fully
understood by references to the following drawings.
FIG. 1 shows a schematic overview of a system and method of
removing a tattoo using a two laser protocol of the present
invention.
A secondary pulsed laser 125 may be used to create a temporary
channel 150 by ablation. The temporary channel 150 may lead from
the surface of the skin 155 of a patient to a granule of tattoo
pigment 140 lying within the dermal layer 145.
An ultra-short pulse main laser 105 may then be used to initiate a
multi-photon process 160 in a vicinity of a granule of tattoo
pigment 140. The multi-photon process 160 may then breakup the
granule of tattoo pigment 140 into fragments that may exit the
patient's skin via the temporary channel 150 as a gas or liquid
vapor. Breaking up the granule of tattoo pigment 140 may also
disrupt a light reflecting property of the pigment, so that the
fragments of the pigment may no longer visible to human eyes.
FIG. 1 also shows an optional alignment laser 175 that may, for
instance, be a He--Ne continuous laser having an operational
wavelength in the visible region of the spectrum at 632.8 nm as
well as an optical system 135 for aligning the lasers.
The lasers and their alignment may, for instance, be controlled by
an electronic controller 180 that may include one or more suitably
programmed electronic controllers. The electronic controller 180
may, for instance, control a main laser positioning module 215, a
secondary laser positioning module 248 and an alignment positioning
module 210.
The main laser positioning module 215 may, in turn, control a
main-laser beam-combiner 220 and a main-laser focusing-element 225
that together may bring a main-laser optical axis 230 into
alignment with a common optical axis 205, and focus the main-laser
beam 235 to a focal spot 115 that may be on the surface of the skin
155 or may be on the granule of tattoo pigment 140.
Similarly, the secondary laser positioning module 248 may, in turn,
control a secondary-laser beam-combiner 245 and a secondary-laser
focusing-element 250 that together may bring a secondary-laser
optical axis 260 into alignment with the common optical axis 205
and focus the secondary-laser beam 255 to a focal spot 115 that may
lie on the surface of the skin 155 and may be coincident with the
focal spot of the main laser.
The optional alignment positioning module 210 may control an
optional alignment mirror 195 and an optional alignment focusing
element 185 that may together focus the alignment laser beam 190 to
a focal spot 115 that may be on the surface of the skin 155 of the
patient, and may bring the optional alignment laser optical axis
192 into alignment with the common optical axis 205.
One of ordinary skill in the art will, however, appreciate that the
femtosecond pulses from the ultra-short pulse main laser 105 may be
delivered to the area of interest on the patient via a delivery
optic such as illustrated in FIG. 1 and/or by a fiber optic or some
combination thereof. The fiber optic may, for instance, also
deliver the main-laser beam 235 through the channels created by the
secondary-laser beam 255.
FIG. 2 shows a schematic view of a laser pulse in a graph with the
flux, or number of photons per unit time, plotted against time. The
pulses 170 have an energy, measured in Joules, that is proportional
to the total number of photons in the pulse and may be represented
by the area under the pulse outline. The pulse has a pulse length
110 that is typically taken as the full width of the pulse at half
maximum intensity. Pulse length is measured in seconds. The power
of a pulse is the energy per unit time and is given by the energy
divided by the pulse length and is measured in Joules/second, or
Watts. The intensity of the pulse is given by the power per unit
area of the beam and is typically greatest at the focal spot and is
given by the power divided by the area of the focal spot and is
measured in Watts/m.sup.2, or as W/cm.sup.2.
FIG. 3 is a schematic drawing of an exemplary device of the present
invention for providing a channel in the skin with nsec-type laser
pulses from a secondary-laser beam 255, while the channel enables
fast access for ultrashort and very high intensity laser pulses for
multi-photon treatments, including the removal of pigments and
tattoo inks, from a main-laser beam 235. The multi-photon
processing treatment device includes a very high intensity
femtosecond laser and associated delivery optics for it.
The delivery optics may, for instance, include a secondary-laser
mirror 222 and a main-laser beam-combiner 220 which together may
align a secondary-laser optical axis 260 and a main-laser optical
axis 230 along a common optical axis 205. The delivery optics may
also include a secondary-laser focusing-element 250 that may focus
the secondary-laser beam 255 to a focal spot 115, and a main-laser
focusing-element 225 that may focus the main-laser beam 235 to a
focal spot 115 that may be coincident with the focal spot formed by
the secondary-laser beam 255.
The femtosecond main-laser beam 235 may, for instance, be from a
suitably configured Titanium doped sapphire (Ti:Sapphire) solid
state laser as supplied by, for instance, COHERENT Inc, of Santa
Clara, Calif. Such a laser may be operating at near infra-red
wavelengths centered at 800 nm and emitting femtosecond pulses
having pulses with a temporal duration in the range of 50 fsec and
100 fsec, a pulse energy of 0.5-5 mJ per pulse and a repetition
rate of 10 Hz-100 Hz, and up to 1 kHz with up to 3 mJ pulse
energy.
The femtosecond main-laser beam 235 may instead be from a suitably
configured laser made using Cr doped Forsterite, or Er- and
Yb-doped fibers, or some combination thereof.
The femtosecond pulses may be delivered to the area of interest on
the patient via a delivery optic and/or a fiber optic through the
channels created by the Secondary Laser beam pulses, for example
nsec- or sub-nsec-type laser beams. FIG. 3 shows delivery optics
for both the secondary-laser beam 255 and the main-laser beam 235.
The ultrashort and nsec-type laser beams may be of different
wavelengths, for example, the nsec-type secondary-laser beam 255
may have a wavelength of 1064 nm and ultrashort main-laser beam 235
may have a wavelength of 800 nm. The nsec-type secondary-laser beam
255, that may for example, have 10 nsec pulses, may be focused by
secondary-laser focusing-element 250, may be redirected by full
intensity reflecting secondary-laser mirror 222 and may pass
through secondary-laser mirror 222, which may be an interferometric
mirror, and which may be almost transparent for the wavelength 1064
nm. The Main Laser beam 235 may be focused by main-laser
focusing-element 225, may be redirected by main-laser beam-combiner
220 which may be an interferometric mirror acting as reflecting
mirror at 800 nm, and which may almost fully reflect the Main Laser
beam 235 having wavelength of 800 nm. After passing main-laser
beam-combiner 220 both beams may travel coaxially along a common
optical axis 205 and may be focused below the skin surface into the
material targeted for treatment, for instance an area containing
pigments. The diameter of the Secondary Laser beam may larger than
the Main Laser beam, so said Main Laser beam may travel toward the
targeted area, for instance tattoo inks, through the channel
created by said Secondary Laser beam with little or no
absorption.
When both beams have the same wavelength, the optical scheme in
FIG. 3 may be modified as illustrated in FIG. 4 and FIG. 5. The
main difference between FIG. 4 and FIG. 5 is in the use of an
optical scheme having the focusing element with a through-hole 270
be an Axicon 273, or conical lens, with a hole in its center
instead of a lens 271 made of spherical surfaces and also with hole
in its center. In both optical schemes of FIGS. 4 and 5 the
secondary-laser beam 255 may first be reflected by secondary-laser
mirror 222 that may be angled at approximately 45 degrees with
respect to the secondary-laser optical axis 260. The
secondary-laser beam 255 may then pass through the Beam Splitter,
or main-laser beam-combiner 220, and may then be focused by a
focusing element with a through-hole 270. The focusing element with
a through-hole 270 may, as shown in FIG. 4, be a lens 271 made of
spherical surfaces, or, as shown in FIG. 5, an Axicon 273, or
conical lens.
In both optical schemes the main-laser beam 235 may first be
focused by main-laser focusing-element 225 and may then travel
through the through-hole in focusing element 270. As stated above,
the focusing element with a through-hole 270 may be a lens 271 made
of spherical surfaces as shown in FIG. 4, or it may be an Axicon
273, or conical lens as shown in FIG. 5.
As in the arrangement of FIG. 3, after passing through the focusing
element with a through-hole 270 both beams may be travelling
coaxially along a common optical axis 205 and may be focused to a
common focal spot 115 that may be located below the skin surface in
the targeted area, that may, for instance, be an area containing
pigments. The focal diameter of the Secondary Laser Beam may be
larger than the focal diameter of the Main Laser beam, so the Main
Laser beam can travel toward the targeted area through the channel
created by the Secondary Laser beam practically without absorption.
In the case when a significantly elongated and uniform channel in
the skin is required, the Axicon 273, or conical lens, of FIG. 5
may be used for focusing the Secondary Laser beam instead of the
lens 271 made of spherical surfaces as shown in FIG. 4.
FIG. 6 schematically illustrates the creation of a channel 150 in
human skin from its surface 155 to the targeted area. Channels 150
may be created using the secondary-laser beam 255, and may allow
for fast access of the main-laser beam 235, which may include
ultrashort and very high intensity laser pulses into the area of
interest, for breaking pigments 320 into small particles and
breaking bonds of large molecules. The channel created by the
Secondary Laser beam with the Main Laser beam concentrically
located inside the channel and reaching the area for multi-photon
interaction with tattoo inks is illustrated.
The tattoo may, for instance, be made up of one or more granules of
tattoo pigment 140, that may include a variety of tattoo inks such
as, but not limited to, black tattoo ink 320, blue tattoo ink 290,
red ink, green ink, or some combination thereof.
The tattoo may be located within the dermal layer 145 that lies
immediately beneath the epidermis 265 and the surface of the skin
155. The epidermis thickness 305 in regions of normal placement of
tattoos, i.e., arms, legs, back, face, torso, is typically about
100 .mu.m. The dermal thickness 310 in these regions is typically
about 4 mm.
The epidermis 265 may contain naturally occurring pigments such as,
but not limited to, melanin 275 that absorbs incident light. The
dermal layer 145 may contain other vessels such as, but not limited
to, hemoglobin 315.
Light may interact with the skin in a number of ways such as, but
not limited to, reflectance 280 off the dermal surface 155,
absorption 285 by the epidermis 265, and dermal and epidermal
remittance 295.
In order to minimize the skin's light attenuating mechanisms such
as, but not limited to, those listed above, the method of the
present invention may use a secondary-laser beam 255 to create a
temporary channel 150. This temporary channel 150 may then be used
to allow and to guide propagation of a main-laser beam 235 to a
vicinity of the granule of tattoo pigment 140, where the main-laser
beam 235 may be focused to an intensity sufficient to initiate a
multi-photon process 160, as described in detail above. The
multi-photon process 160 may break up the granule of tattoo pigment
140, including any black tattoo ink 320 or blue tattoo ink 290
particles that may be sufficiently close, as also described
above.
The fragments of pigment and pigment molecules may escape via the
temporary channel 150 into the atmosphere, or they may also, or
instead, diffuse down through the dermal layer to blood vessels
located beneath.
The tattoo removal process may include repeating breaking the
granules of tattoo pigment until the remnants of the granules of
tattoo pigments leave no visible sign of a tattoo. One measure of
the tattoo being removed may be that any tattoo pigments that may
remain, produce substantially no reflection of visible light
observable by a human observer having 20/20 vision at light levels
of 750-1000 lux.
FIG. 7 shows a close up schematic cross-sectional view of two laser
tattoo removal in accordance with a further embodiment of the
present invention in which a second-laser beam 235 may be focused
through a temporary channel 150 that may have been created by a
first-laser beam 255. The temporary channel 150 may extend from the
surface of the skin 155 through the epidermis 265 to a granule of
tattoo pigment 140, typically located near an upper region of the
dermal layer 145.
The focused second-laser beam 235 may be sufficiently intense to
initiate a multi-photon process 160 that may break up the granule
of tattoo pigment 140.
The surface of the skin 155 in a region including the temporary
channel 150 may be covered by a layer of water-impermeable material
325 that may be substantially transparent to both the first-laser
beam 255 and the second-laser beam 235.
The layer of water-impermeable material 325 may reduce any loss of
moisture from the skin during the creation of the temporary channel
150 or during the multi-photon process 160 breakup of the granule
of tattoo pigment 140.
The layer of water-impermeable material 325 may be any suitable
material such as, but not limited to, a mm or thinner layer of
mica, a polymer coated onto the skin surface, a gel, a thin glass
or plastic plate, or some combination thereof. In a further
preferred embodiment of the invention, the layer of
water-impermeable material 325 may be a sheet of mica having a
thickness of 100 .mu.m or less.
Examples of Use of the Invention
In a first test, Example 1, two laser beams with very different
pulse durations, whereas approximately 100 fsec of very high
intensity laser pulses, for example an intensity on pigments or
inks inside the skin of more than 10.sup.12 W/cm.sup.2, were
applied for multi-photon processing via the main laser, and
approximately 10 nsec low intensity pulses from the secondary laser
created elongated channels in the skin. The main laser was
Ti/Sapphire laser with a wavelength of 800 nm and the secondary
laser was a 10 nsec Nd/YAG laser with a 1064 nm wavelength. Both
lasers were run at a 10 Hz repetition rate. Because of the
significant difference in the wavelengths, the optical scheme of
FIG. 3 was applied. The 100 fsec laser pulses were directed to
tattoo inks via channels created in the skin by 10 nsec pulses. The
pulses of both lasers were synchronized. The 100 fsec pulses were
reaching tattoo inks practically without absorption while traveling
to the inks and were breaking the inks into small particles and
large molecules to small ones by a multi-photon process. The
shattered remnants were leaving the tattoo ink areas to outside the
skin through the channels and diffusing inside the skin into blood
streams. This test of the invention demonstrated removal of a
7-color tattoo from a small testing area of about 1 cm.sup.2 in
just several sessions without scarring.
Additional testing was performed using lasers with 100 Hz and 1 kHz
repetition rates, but with about 10-20 times significantly lower
energies per pulse for each laser. Results for tattoo removal were
similar to those presented above, although the rate of removal
tattoo was not proportional to repetition rates of the lasers.
In a second test, Example 2, two laser beams with the same
wavelength were used. Both the optical schemes shown in FIGS. 4 and
5 were tested. As in Example 1, the two laser beams had very
different pulse durations. The tests demonstrated the removal of
multi-color tattoos. The optical scheme of FIG. 5 provided similar
results to those using the optical scheme of FIG. 4, but did not
require moving the lens 271 made of spherical surfaces along the
axis of the secondary laser beam to create sufficiently long
channels in the skin. Of course, movement of lens 271 along the
axis of the secondary laser beam, which is the common axis for both
laser beams, did not affect the main laser beam, which was
traveling inside the hole in the lens without interacting with said
lens. Similarly, as in Example 1 that employed the optical scheme
shown in FIG. 3 above, the Main Laser's approximately 100 fsec
ultrashort and very high intensity laser pulses of 10.sup.12
W/cm.sup.2 or greater on the pigment or inks were applied for
multi-photon processing. The 100 fsec laser main laser was
Ti/Sapphire with a wavelength of 800 nm. For convenience, the
secondary laser beam's nsec-type pulses also had a wavelength of
800 nm. This was the result of the second beam being obtained by
splitting an 800 nm laser beam before the compressor, where the
pluses are about 0.2 ns in temporal duration. This beam was focused
with the lens 271 made of spherical surfaces and which had a
centered through-hole. The second part of the beam was compressed
down to .about.100 fsec and then focused by the main-laser
focusing-element 225. The focusing main-laser beam was propagated
through the hole in the focusing element with a through-hole 270
that in the optical arrangement of FIG. 4 was a lens 271 made of
spherical surfaces, and in the optical arrangement of FIG. 5, an
Axicon 273, or conical lens. The main-laser beam 235 was focused in
to the channel created by the secondary-laser beam 255, directly
onto the skin pigments or tattoo inks, which were disintegrated by
means of multi-photon processes. In both cases, the Ti/Sapphire
laser used to generate both the main-laser beam 235 and the
secondary-laser beam 255 was running at a repetition rate of 5 Hz
with a minimum energy for each beam of about 10 mJ/per beam per
pulse and up to 30 mJ/per beam per pulse.
Creation of white spots on the surface of the skin has been
observed as a result of applying the Secondary and Main Lasers.
Focusing the Secondary and Main Laser beams through glass or mica
before said beams reach the skin decreased the intensity of the
white spots. Glass was typically 150-200 .mu.m thick and mica was
as thin as 50 .mu.m, although other thicknesses could be used. Both
glass and mica have very good transparency for the Main Laser beam,
operating at the wavelength of 800 nm and the Secondary Laser beam
operating at the wavelength of 1,064 nm. However neither regular
glass nor mica are transparent for deep UV radiation, hence
protecting skin from burning by UV radiation from plasma created on
surface of skin by Main Laser beam pulses.
Clinical Use
A clinical use of the multi-photon processing systems of present
invention can be similar to this as presented in U.S. Pat. No.
8,187,256, which is incorporated herein, but slightly more
complicated due to use of two laser beams instead one beam. In a
preliminary examination, a tattoo may first be evaluated in terms
of the relevant variables, which include the extent of the affected
region, the depth of the ink layers, and the types of inks used in
the tattoo. Other factors, such as the natural skin color
surrounding the tattoo, the age of the patient, the quality of
natural wound healing, and other factors including the patient's
general health may be noted. A map of the tattoo may then be
created, for example, from a white light image of the tattoo
obtained by, for instance, a camera, that may be a CCD camera, and
the imaging telescope operating under the control of a computer.
Using image processing techniques, details of the physical location
of the tattoo pigments may be obtained, including the depth of the
pigmented layers. However, in contrast to using only a single
ultrashort and very high intensity laser beam, by using the
additional Secondary Laser beam for creating the channel in the
skin, a patient-specific procedure for the tattoo removal could be
less sensitive to the above-mentioned patient conditions.
In a manual treatment, the operator may choose the laser parameters
such as, but not limited to, the power per shot, the number of
shots, the repetition rate, the positioning, and the focusing
requirements of the laser beam. The operator may then apply the
ultrashort ultra very intense laser pulses to the area of interest
being treated by multi-photon processes using a delivery optical
system. Progress may be monitored by, for example, direct visual
inspection, or by the use of a camera that may connected to a
viewing monitor by means of a computer.
In a computer-controlled treatment, the delivery optical system can
direct the Secondary Laser beams and the Main Laser beams to the
area by, for example, an optics positioning system that may be part
of the positioning unit. The operator may monitor progress by, for
example, direct visual inspection, or by the use of a camera that
may be connected to the viewing monitor. The camera may also be
used in all treatments, manual or computer-controlled, to obtain
and store still or video images and to record the progress of the
removal procedure.
The treated area may be evaluated after one round of laser
ablation. A further treatment may be advised, either immediately
following the first treatment, or after one or more days. Based on
experiments described above, it is expected that most individuals
may only need just a few treatments in period of a several weeks
but said period could be as short as one or two weeks.
Testing of this invention has shown practically total removal of a
so called "professional tattoo" (which are different to "amateur
tattoo" in that the ink is typically placed at a more shallow
location beneath the skin than in professional tattoos) of 7 colors
from small testing area without any significant pain, skin damage,
or post-treatment scars.
Although the invention has been described in language specific to
structural features and/or methodological acts, it is to be
understood that the invention defined in the appended claims is not
necessarily limited to the specific features or acts described.
Rather, the specific features and acts are disclosed as exemplary
forms of implementing the claimed invention. Modifications may
readily be devised by those ordinarily skilled in the art without
departing from the spirit or scope of the present invention.
* * * * *